Solar flare radiation expected to hit

The largest solar flare in four years erupted Monday. Its radiation is expected to reach Earth today and Friday and perhaps interfere with communication systems, power grids and navigation satellites. It might also enhance the northern lights.

Radiation from the largest solar flare in four years is expected to reach the Earth Thursday and Friday, potentially interfering with communication and navigation satellites and disrupting ground-based communication networks and power grids.

The rain of charged particles from the so-called coronal mass ejections, or CMEs, should also enhance the northern lights, also known as the Aurora Borealis, making them both more prominent and visible farther south, perhaps even into the northern tier of the United States, experts said.

The solar flare, which erupted Monday, occurs when magnetic field lines on the sun's surface in effect get short-circuited, releasing large amounts of energy into space. Three such events occurred Monday, the largest of them a so-called class X event — the most powerful form of solar flare. Astronomers have been expecting the sun to ramp up its activity after several years of quiescence during its normal 11-year cycle of activity. Maximum solar activity is expected in 2013.

Eight minutes after the bursts, X-rays traveling at the speed of light struck the Earth. But the charged particles released during the eruptions take longer to travel the 93 million miles separating the two bodies and are not expected to begin arriving until sometime midday Thursday.

Some may have already gotten here, however, as China has reported disruptions of radio communications in the southern part of the country.

The disruptions are not expected to be as severe as some past events. In 1972, a solar flare shut down telephone lines in the state of Illinois and another flare in 1989 knocked out power for 6 million people in the Canadian province of Quebec.

Researchers and industries will have about a 30-minute warning that the CMEs are going to strike from a NASA satellite called the Advanced Composition Explorer, which monitors the solar radiation.